The invention is in the field of ferrophosphorus metal alloys and their use to control the development of cracks that form during the early phases of cure in cement composites. More particularly, this invention relates to specific amorphous ferrophosphorus-based alloys and the use of the alloys in wire, ribbon, and fiber forms, to control, reduce, eliminate, or retard the growth of cracks in cement composites.
Cement composites are typically cements, mortars, and concretes. Minimally, cement composites are non-homogeneous mixtures of cement, sand, aggregates and water. Cement composites may also include a number of additives or admixtures that impart important chemical and physical properties to the composites such as improved rheology, impact strength, flexural strength, and resistance to permeability. The additives and admixtures include water reducing admixtures, metal and nonmetal fibers, polymers, silica fume, and the like.
After the cement composite is poured or placed in its final form, the composite undergoes a relatively rapid loss of water over of period of 24 to 48 hours. The loss of water is primarily due to evaporation from the exposed surfaces of the cement composite. The loss of water requires waiter migration within the composite, this process is a non-uniform or non-isotropic process. This factor coupled with the non-homogeneous nature of the cement composite contributes to the formation of non-equilibrium stresses. The stresses lead to the formation of cracks that are frequently referred to as plastic shrinkage cracks and plastic settlement cracks.
Several authors have recently attributed the formation of cracks during the early phases of cement composite curing to the majority of failures in bridge decks as well as the lack of overall durability in modern concrete structures. Articles by Khossrow Babaei and Amir M. Fouladgar ("Solutions to Concrete Bridge Deck Cracking", Concrete International, July 1997, pp 34-37) and P. Kumar Mehta ("Durability--Critical Issues for the Future", Concrete International, July 1997, pp 27-33) are examples of an expressed need for solutions to the problem of plastic shrinkage cracking and plastic settlement cracking. For the purpose of this invention, "shrinkage cracks" refers to plastic shrinkage cracks or plastic settlement cracks which occur in cement composites during the first 24 to 48 hours of cure of the cement composites, and control of shrinkage cracks refers to the elimination, reduction, retardation in growth or ability to prevent shrinkage cracks.
Once a crack has formed in a cement composite, the crack serves as a point of entry for water, road salts, and other environmental influences that can damage the composite in both an acute and chronic manner. Water intrusion and cycling of temperatures below and above the freezing point of water results in a phenomena commonly referred to as freeze-thaw damage. Road salts can penetrate cracks and corrode reinforcing steel or bars (rebar) imbedded in the cement composite. Each process serves to gradually increase the size of the original cracks and permit intrusion and penetration of increased amounts of water and salt into the composite. Ultimately, the cement composite is weakened and has a reduced capacity to withstand the stresses the composite was designed to bear. The weakened composite may require early repair, partial or full replacement, or it may fail catastrophically.
Fibers are added to cement composites to improve durability. Steel fibers (which are crystalline) are added to improve the flexural strength durability of the cement composite. Synthetic fibers, sucht as polypropylene and nylon, are added to improve the control of cracks that form during the curing of the cement composite. Steel fibers are sometimes added to improve the control of cracks that form during curing, but the addition levels are so large (10 to 100 lb. of fiber per yd.sup.3 of composite) that the rheology of the composite is impaired. The impairment of rheology is overcome by the addition of admixtures, namely surfactants, such as naphthalenic surfactants. If the impairment of rheology is not overcome, the cement composite is stiff and does not pour well. Ultimately, the cement composite will fail due to the inability to properly place and finish the composite.
Thus, it would be desirable to produce a steel fiber that controls the formation of cracks during cement composite curing; at addition levels that are less than about 10, preferably less than about 5 lbs per cubic yard of cement composite. Or, conversely, it would also be desirable to produce a steel fiber that controls the formation of cracks during cement composite curing at addition levels similar to the addition levels that are used for current commercially available crystalline steel fibers without the requirement for an admixture to overcome the deleterious affect on rheology.